Drop on demand inkjet technology has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an inkjet image is formed by the selective activation of inkjets within a print head to eject ink onto an ink receiving member. For example, an ink receiving member rotates perpendicular a print head assembly as the inkjets in the print head are selectively activated. The ink receiving member may be an intermediate image member, such as an image drum or belt, or a print medium, such as paper. An image formed on an intermediate image member is subsequently transferred to a print medium, such as a sheet of paper, or a three dimensional object, such as an electronic board or bioassay.
FIGS. 4A and 4B illustrate one example of a single inkjet ejector 10 that is suitable for use in an inkjet array of a print head. The inkjet ejector 10 has a body 48 that is coupled to an ink manifold 12 through which ink is delivered to multiple inkjet bodies. The body also includes an ink drop-forming orifice or nozzle 14 through which ink is ejected. In general, the inkjet print head includes an array of closely spaced inkjet ejectors 10 that eject drops of ink onto an image receiving member (not shown), such as a sheet of paper or an intermediate member.
Ink flows from the manifold to nozzle in a continuous path. Ink leaves the manifold 12 and travels through a port 16, an inlet 18, and a pressure chamber opening 20 into the body 22, which is sometimes called an ink pressure chamber. Ink pressure chamber 22 is bounded on one side by a flexible diaphragm 30. A piezoelectric transducer 32 is rigidly secured to diaphragm 30 by any suitable technique and overlays ink pressure chamber 22. Metal and polymer film layers 34 that can be coupled to an electronic transducer driver 36 in an electronic circuit can also be positioned on both sides of the piezoelectric transducer 32.
Ejection of an ink droplet is commenced with a firing signal. The firing signal is applied across metal film layers 34 to excite the piezoelectric transducer 32, which causes the transducer to bend. Upon actuation of the piezoelectric transducer, the diaphragm 30 deforms to force ink from the ink pressure chamber 22 through the outlet port 24, outlet channel 28, and nozzle 14. The expelled ink forms a drop of ink that lands onto an image receiving member. Refill of ink pressure chamber 22 following the ejection of an ink drop is augmented by reverse bending of piezoelectric transducer 32 and the concomitant movement of diaphragm 30 that draws ink from manifold 12 into pressure chamber 22.
To facilitate manufacture of an inkjet array print head, an array of inkjet ejectors 10 can be formed from multiple laminated plates or sheets. These sheets are configured with a plurality of pressure chambers, outlets, and apertures and then stacked in a superimposed relationship. Referring once again to FIGS. 4A and 4B for construction of a single inkjet ejector, these sheets or plates include a diaphragm plate 40, an inkjet body plate 42, an inlet plate 46, an outlet plate 54, and an aperture plate 56. The piezoelectric-transducer 32 is bonded to diaphragm 30, which is a region of the diaphragm plate 40 that overlies ink pressure chamber 22.
One goal of print head design is to provide increasing numbers of inkjet ejectors in a print head. The more inkjet ejectors in a print head, the greater the density of the ink ejected and the perceived quality of the image. One approach to increasing inkjet ejector density in a print head is to locate the manifold external of the inkjet ejector. One way of implementing this approach includes providing an inlet in the diaphragm layer for each ejector. Coupling the inlet to the manifold to receive ink for ejection from the ejector, however, requires an opening in the piezoelectric-transducer layer to enable ink flow from the manifold to the inlet and then into the pressure chamber in the inkjet body plate. Each opening in the piezoelectric-transducer layer is located in a polymer portion in the interstices between the piezoelectric transducers.
In the assembly of previously known layered print heads having piezoelectric actuators, the process of mounting the layer containing the piezoelectric actuators and polymeric interstitial material to the diaphragm layer requires the use of a liquid thermoset polymer. This thermoset polymer spreads and enters the openings in the piezoelectric-transducer layer and the inlets in the diaphragm layer and then cures. The cured thermoset polymer then blocks the ink flow path into the inkjet ejector. Removal of the cured thermoset polymer from the ink inlets is difficult. To facilitate the removal of cured thermoset polymer from the inlets of the diaphragm plate, a print head assembly method has been developed that blocks the thermoset polymer from migrating past the diaphragm plate and enables the cured thermoset polymer to be removed from the inlets in the diaphragm plate by laser ablation. This method also makes possible the filling of the interstices between the piezoelectric transducers with thermoset polymer after the piezoelectric transducers have been mounted to the diaphragm plate. During this process, however, thermoset polymer reaches a level that covers an upper surface of the piezoelectric transducers and electrically isolates the transducers. This electrical isolation hinders the electrical connection of the piezoelectric transducers to the firing signals for operation of the print head.